This invention relates to electrochemical cells of improved construction. Specifically, it is concerned with cells having an improved seal in the fill opening of the cell container. The fill opening is utilized for the introduction of cell components into the cell container. It is sometimes also referred to as a "fill port".
With the advent of high energy density nonaqueous cells generally utilizing fluid components such as thionyl chloride and sulphur dioxide depolarizers and various reactive organic electrolyte solvents, the design and sealing of the fill opening in such cells has become increasingly important. For purposes of this invention, the term "fluid" is meant to describe any component capable of flowing through a fill port and into a cell container. In most instances, the component will be a liquid, including solutions.
It should be understood that, if a fluid component is used in accordance with this invention, it need be in fluid form only at the time of its introduction into the cell container. Thereafter, it may solidify or assume any other form as required by the particular cell involved.
Electrochemical cells such as rechargeable lithium cells having a liquid electrolyte and incorporating various components may make use of the invention. For example, see U.S. Pat. Nos. 4,118,550 and 3,998,658 for cells of this type. The following listed U.S. patents show various lithium-halogen batteries or cells of another type making use of cell containers in which a fluid component is introduced in the container through a fill opening: U.S. Pat. Nos. 4,105,833; 4,135,519; 4,132,836; 4,166,887; 4,211,832; 4,360,573; 4,611,395, and 4,748,094. These cells may also make use of this invention. All of these patents are incorporated herein by reference.
In such cells it is important to assure hermetic sealing of the fill port. It is also important to provide means for assuring that a hermetic seal has been completed upon sealing the fill port. The contents of such cells typically may consist of high energy corrosive materials such as lithium anodes, carbon current collectors and liquid thionyl chloride cathode/electrolytes and the like. Other such cells may include lithium anodes, organic solvent electrolytes such as propylene carbonate containing a dissolved salt such as lithium perchlorate for enhanced conductivity, and solid cathode materials such as manganese dioxide, vanadium pentoxide or carbon monoflouride. Other such cells may contain cathode depolarizer materials such as organic-iodine charge transfer complex compounds.
Such cells are usually encapsulated in a metal container which, as already stated, includes a fill port. Stainless steel is the metal most commonly used. Following placement of mechanical parts and any solid chemical constituents in the container, the container is then closed with a container cover. Typically the fill port is located in the cover. The container is then filled with any liquid or liquid-like battery constituents, such as fluid cathode/electrolytes in the case of thionyl chloride batteries or molten charge transfer complex in the case of iodine batteries, by pouring same into the cell container through the fill port. The fill port is then closed and sealed.
The hermeticity or perfection of seal at the fill port is an important feature, particularly in such high reliability cells. It is also important that the seal be amenable to testing in order to ascertain and demonstrate that a high degree of hermeticity has been achieved.
A seal arrangement for this purpose which has been used extensively comprises a double seal arrangement having inner and outer seals in the fill port with an intermediate space therebetween containing a means such as glass bubbles for holding a test gas used in testing the outer seal for hermeticity. Such an arrangement facilitates the hermetic testing of the outer seal thereby providing a basis for a high degree of confidence in its hermeticity.